This application claims priority from Canadian Patent Application No. 2,337,284 to Dofher, entitled xe2x80x9cSubsurface Fibre Optic Cable Network Installationxe2x80x9d filed Feb. 15, 2001.
The present invention relates to subsurface installation of fibre optic cables, for example, in urban settings where cable is laid buried under the surfaces of streets or sidewalks. As well, the invention relates to fibre optic cable installation within masonry construction and other construction, as well as systems for forming a branching fibre optic cable network.
With the rapidly growing need for high-speed data connections to businesses and residences (driven mainly by the need to access the Internet) a faster and more economical method is needed in order to deliver these connections. Optical fibre offers the greatest potential to deliver high-speed services due to its ability to carry high bandwidth over long distances. One problem that the telecommunications industry has been faced with is the high cost of installing optical fibre between the provider and the end customer. This issue has restricted the expansion of optical networks to very densely populated regions where the economics can justify the expensive conventional construction process of burying cable within a relatively large trench.
It has been suggested that an inexpensive and simple means to lay cable is within a shallow slit-like trench cut into an upper layer of pavement or the like, for the laying of a cable within or immediately under a street or other surface. Such a system requires a convenient means to form junctions or branches within the cable system. In conventional cable-laying systems or methods, the forming of a branching network requires considerable additional excavation in order to install conventional junction boxes or the like.
It is desirable to provide a simple and inexpensive system for installing a branching-type network of fibre optic cables within a variety of surfaces. One approach that is known is to install cable within narrow slit-like trenches or recesses that are cut, for example, into street surfaces. Such an arrangement should also provide a convenient means for subsequent location of intersection points, as well as providing for future expansion of the cable network. For the latter, it is important that this system provide an easy means to provide cable slack without requiring the labour-intensive job of splicing of cables to meet future system needs.
Further, it is desirable to provide a junction box or branching node that readily fits within a narrow slit like trench or groove without requiring substantial additional excavation, and which further is easy to install and subsequently locate.
Several patents have been issued for technology relating to electrical and optical fibre cable installations.
One example is U.S. Pat. No. 5,879,109 issued to Finzel, et al. which provides a complex process for installing optical or electrical cable into solid surfaces such as asphalt. The method uses a slow moving apparatus to heat the ground surface until it has softened. A channel-forming unit is subsequently used to introduce a channel into the heated ground by displacing the ground material alongside the channel border. A laying unit is then used to introduce the optical or electrical cable into the channel, followed by a filling unit which is used to reintroduce the displaced ground material back into the channel and then rolled to compact the ground material which has been reintroduced into the channel. However, the complexity of this method if used for small segment connections between end customers and providers of optical fibre cable within confined urban locations and in a variety of infrastructure materials would make it prohibitively expensive. Also, this method does not work in concrete material as found in sidewalks, curbs and grout lines, which are often preferred routes in most last mile deployments.
In another example, U.S. Pat. No. 6,065,902 issued to Mayr, et al. provides a method and apparatus for on-site production and installation of optical fibre cable at the location for placing. This method seeks to reduce transportation costs and quantity of material required for large-scale optical fibre cable installations. However, for small-scale installations this method is impractical and notably more expensive.
Canadian published application no. 2,237,324 (Zeidler et al) discloses a method for laying a thin fibre optic cable of between 2 mm and 10 mm, within a narrow channel having a width slightly wider than the cable. The cable is introduced into the channel by means of a cable feed device, and is filled with infill material by a filling device which moves along in a coordinated fashion with the laying device. The laying channel extends into the top several layers of a paved surface and is between 4 cm and 15 cm in depth, with 7 cm being identified as ideal.
The prior art systems and methods tend to be complex, expensive and do not suitably provide for several needs. There is a need for a convenient arrangement for forming cable junctions. There is a need to easily provide slack in the installed cable to accommodate junctions, system expansions and repairs. There is a further need to easily accommodate a variety of surfaces including pavement, sidewalks, vertical walls, unpaved surfaces such as sod, etc.
The objects of this invention are to provide improved methods and systems for installing cable within a narrow, shallow trench; to provide a convenient cable junction system; and to provide means to accommodate future system expansion. In accordance with the above objects, the present invention comprises in one broad aspect a method for laying or installing of a cable such as a fibre optic cable, or a branching network of fibre optic cables within a surface or substrate such as a paved roadway, a masonry wall or other hard or soft surface. The term xe2x80x9csubstratexe2x80x9d herein means any surface, whether a roadway, walkway, wall or the like.
It is contemplated that system xe2x80x9cnodesxe2x80x9d are provided at intervals within the cable network system. A node may comprise a cable junction or a region of looped cable that may be used to provide cable slack for future node or junction installation or other system expansion. In this aspect, the method consists of the steps of:
cutting a narrow channel or groove within a surface such as pavement or other ground surface or a portion of a building or residential unit;
installing a fibre optic cable within the narrow channel;
providing at periodic convenient locations one or more system nodes by installing within the channel at such locations a loop of cable, and optionally a junction box, and connecting to said junction box on opposing sides of an incoming cable and two or more outgoing cables; and
backfilling and sealing said channel or groove.
The channel typically has a width between nodes of between about 1 mm and 50 mm with a preferred range of between 2 mm and 12 mm. A still more preferred width is between 4.5 mm and 6 mm. The depth of the channel is between about 8 mm and 250 mm, although there is in principle no limit to the depth of the channel and depths up to 1 m are acceptable. The preferred depth range is between 12 mm and 172 mm. A most preferred depth is between 40 mm and 70 mm. Depending on the width of the channel on each side of a node, the channel may be widened at the region of each node, by up to a further 20 mm but preferably by no more than a further 15 mm.
The deeper end of the depth range of the channel (e.g. 50 mm-1 m) is suitable for crossing streets that may get resurfaced in order to survive a pavement grind and overlay. As well, a deeper cut within this same range is desirable if the surface is breaking away or is in generally bad shape. If the surface is sound then the cut may be in the range of 8-50 mm in depth and preferably about 40 mm deep. In another aspect, the blade that is used on the slab saw makes a cut that is about 4.5 mm wide.
The junction box consists of a narrow, generally flat housing having a width suitable for fitting within the narrow channel.
In another aspect, a metal member capable of detection by a metal locating device is incorporated within the junction box or buried within in a node either in the absence of a junction box or in position with the junction box, in order to provide a convenient means for subsequent location of the junction box or node by means of a metal detection device. The metal member may be either non-ferrous or ferrous, or alternatively, a ferrous member may be buried with a non-junction box node and a non-ferrous member with a junction box node, or vice-versa, for differential (i.e. discriminating) detection by different types of metal detectors after burial.
In a further aspect, the channel as described above is formed within the interstices between pavers on a walkway or roadway, or within a masonry wall. In the case of a wall, the channel has a generally horizontal orientation and is formed between adjacent brick layers. In this aspect, the channel has the width described above but the shallower end of the depth range is sufficient, i.e., about 12 mm deep. The channel is then covered with mortar grouting to provide a matching appearance with the remainder of the brick or masonry wall. In a similar fashion, the channel may be formed in the interstices within a brick or stone walkway or roadway.
In a further aspect, the location of the channels within a masonry wall may be indicated by visual indicators and/or metal implants for location by a metal detection device.
In a further aspect, the channel is wholly within a surface region or layer of an asphalt or concrete roadway or sidewalk. In a further aspect, the trench may be cut at or immediately adjacent to the junction of a roadway and a curb, or within an expansion joint between a curb and an adjacent sidewalk.
In a further aspect, a plurality of cables may be laid in overlying relationship within a trench. The plurality may be between 2 and 20 cables, with a preferred array being 2 to 5 cables.
In a further aspect, the trench may be filled with liquid resin or other anchoring cement to form a smoothly finished patch. An example is a two-part polyurethane grout that hardens, but remains flexible. When hardened, this material is very difficult to pick away and seals the cut. In a still further aspect, a wire may be positioned to immediately overly the installed cables to provide a convenient means for removing the overlying patch material for future maintenance. In a still further aspect, a looped portion of fibre optic cable may be formed within a deepened portion of the channel at a location removed from the junction node to provide cable slack for future expansion of the cable network.
In a still further aspect, one or more of the system nodes include between 1 and 20 loops of cable, for providing slack when required for future system needs, with a preferred number of cable loops being between 2 and 5.
In a still further aspect, the invention relates to a junction box for installation within a narrow slit-like channel or trench, as part of a fibre optic branching network or system. In this aspect, the box consists of a housing or case having flat opposing sides with an overall width selected to fit snugly within the trench. Preferably, this width is between 5 mm and 20 mm, and preferably between 8 mm and 12 mm. A most preferred width is about 10 mm to fit within the narrow slit-like trench or channel. The inside cavity is about 6 mm in width to accommodate passive optical components and/or splices. The two sides are joined together by releasable fastening means. Conveniently, the box is generally rectangular in all elevations. An opening at one of the ends of the box permits entry of input cable line. A plurality of openings on a second, opposed end of the box permits the outlet of output cable lines. The inlet and outlet entries are provided on the narrow ends of the box in order to maintain a flat, narrow arrangement when the cables are joined with the box. Sufficient interior space within the junction boxes is provided for joining together the input and output cable ends. As well, passive optical networking components and optical splices may be placed in the box.
In a still further aspect of the above method, one or more loops of cable slack are formed to surround the junction box prior to burial of the node.
A further aspect of the invention relates to a cable-winding device for forming one or more cable loops for installation in a node. The winding device comprises a base having cable-receiving means at either end for winding a length of cable, which may be subsequently removed from the device for burial. Conveniently, rotatable arms at the receiving means releasably retain the cable. A junction box retaining means such as an array of pegs extending from the base may be provided to releasably hold a junction box against the base in position from wrapping cable loops around the box.
A generally rigid frame such as a rigid wire loop may be provided to support the cable loops. By xe2x80x9crigidxe2x80x9d is meant having sufficient rigidity to protect a cable loop from damage. A high degree of rigidity is not necessarily required. The frame has generally the same configuration as the cable loops, and is joined to the base either before or after the loops are wound about the base. The combined looped region of cable and wire frame are then released from the winder for burial. The attached wire frame adds rigidity to the cable loops to prevent inadvertent crushing before or after burial.
A still further aspect of the invention relates to a rigid conduit for burial of cable within a narrow trench or channel set within a soft ground surface such as sod. In this aspect, the conduit comprises an elongate, hollow conduit such as a length of PVC pipe having a channel extending into the interior thereof and extending the full length of the conduit. The conduit may have a generally circular oval or rectangular cross-section. The invention further relates to a method for installing cable within a soft ground surface such as sod by cutting a narrow trench as described above, and installing into the channel one or more fibre optic cables together with an elongate conduit as described above with the channel facing downwardly followed by burial of the conduit to restore the surface.
A further aspect consists of a fibre optic cable comprising a substantially waterproof outer casing, a fibre optic core, and an absorbent material within the interior of the cable, such as a string having a super-absorbent polymer embedded in its fibres.
The terms xe2x80x9cbasexe2x80x9d, xe2x80x9ccapxe2x80x9d and like references are not intended to refer to any particular spatial position of any component but are used herein to refer to various components purely for ease of description.
The term xe2x80x9capproximatelyxe2x80x9d or like terms herein mean plus or minus 10 per cent.